1. Technical Field
The technical field relates to an imaging device, and more particularly relates to a single lens reflex digital camera.
2. Background Information
Single lens reflex digital cameras, with which an optical image of a subject can be converted into an electrical image signal and outputted, have exploded in popularity in recent years. With these single lens reflex digital cameras, when the user views a subject through a viewfinder, a reflecting mirror is provided along an imaging optical path between an imaging lens and an element. The light incident on the imaging lens, that is, an subject image is reflected by a reflecting mirror to change its optical path, and is passed through a pentaprism or the like to create a positive image, and guided to the optical viewfinder. This allows the user to view the subject image through the imaging lens from the optical viewfinder. Therefore, the position where the viewfinder-use optical path is formed is usually the home position of the reflecting mirror.
Meanwhile, when the imaging lens is used to capture an image, the reflecting mirror instantly changes position and is retracted from the imaging optical path, so the viewfinder optical path is switched to the imaging optical path, and the mirror instantly returns to its home position once imaging is complete. With a single lens reflex camera, this operation is the same regardless of whether the camera is a conventional silver halide camera or a digital camera.
Also, a retractable sub-mirror is provided along the imaging optical path between the reflecting mirror and the imaging element. The sub-mirror is located along the imagine optical path during focal length measurement, and reflects the light incident on the imaging lens and guides it to a focal length measurement component. The focal length measurement component measures the focal length by a phase difference detection method, for example. The measured focal length is used for focal point detection.    Patent Citation 1: Japanese Laid-Open Patent Application 2001-125173
Thus, with a conventional digital single lens reflex camera, there was a space between the imaging lens and the imaging element which housed a reflecting mirror for forming the viewfinder optical path and a sub-mirror for forming the focal length detection optical path. Therefore, the size of the camera body could not be reduced in the optical axis direction (that is, the direction along the optical axis of the mounted interchangeable lens).
In view of this, there has been a proposal for a single lens reflex digital camera with which focal point detection is performed by a contrast detection method, so that there is no need to dispose a reflecting mirror and sub-mirror.
However, it is conceivable that an interchangeable lens and a camera body that each have a different focal point detection method may be combined. For instance, if an interchangeable lens that is not compatible with a contrast detection method is mounted, there is the risk that the camera body will not be compatible, and this makes the product less convenient to use.